numZonesClosed

How many zones are held by something other than a vehicle.

The statistic that makes the whole construct validatable, and the reason it is here rather than on the zones: there are thousands of zones and a handful of occupiers, so this is one response for the space instead of one per zone. Its time-average is the mean amount of guide path closed to traffic over the run, which is exactly the quantity a model without spills or closures has to hide inside inflated task times.

Separate from zoneUtilization, which counts vehicle bodies. Three different things can now make a zone unavailable -- a vehicle, an occupier, a population -- and collapsing them into one number would lose the decomposition that this work exists to expose.